INDIANAPOLIS (AP) — Mike Braun, the Republican candidate for a crucial Senate seat in Indiana, often refers to his rival, Sen. Joe Donnelly, as "Sleepin' Joe" and has vowed to wake the vulnerable Democrat from his "siesta" on Election Day.

But as Donnelly barnstorms the state in a used RV, it is Braun's own sleepy campaign that's leaving Republicans underwhelmed — and worried.

Groups that typically back GOP candidates, such as the Indiana Chamber of Commerce, are sitting on the sidelines. Braun's recent three-stop "solutions" tour — spread out across three days — was ridiculed by Democrats, who pointed to Donnelly's seven-day, 40-stop trek in August.

And while Braun, a multimillionaire businessman, took out $6.4 million in loans to fund his primary campaign, he also publicly groused about the cost. Now, with less than two months until the election, he has yet to purchase air time for October, while Donnelly has outspent him by almost double on TV and radio since June, records show.

That's cause for concern, according to a half-dozen GOP officials, operatives and commentators familiar with the race, most of whom spoke to The Associated Press on condition of anonymity to offer candid assessments of the contest. They say Braun appears to be coasting at a time when he ought to be investing more of his own money and rallying the base.

Conservative talk radio host Rob Kendall summed up the GOP's worries by pointing to Braun's recent appearance with President Donald Trump at a rally in Evansville.

"He's in front of (thousands of) people at the Ford Center and it sounds like you're at a funeral," said Kendall, who is a producer and has a show on Indianapolis-based WIBC radio. "I would have been like James Brown and the Blues Brothers shouting out 'Do You See the Light' to the congregation. And this guy, you have to check him for a pulse."

Republicans have viewed Donnelly's seat as a prime pickup opportunity in a state Trump won by nearly 20 points in 2016. The criticism of Braun's performance reflects a sudden sense among the GOP that Senate contests in several states Trump carried may be tougher than expected and that control of the Republican-led chamber could be at stake — a prospect that was unthinkable just a few weeks ago.

"Mike gets things done, and Donnelly is the least effective Democrat in the Senate," Braun spokesman Josh Kelley said in a statement. He noted that Braun "has held 80 grassroots events since the primary — including two packed rallies with President Trump — reminding Hoosiers of Donnelly's liberal record of voting for Obamacare and against tax cuts."

The race was thrown into further chaos this week after an allegation of decades-old sexual misconduct surfaced against Trump's Supreme Court nominee, Brett Kavanaugh. The development could cut both ways in the race, potentially hurting Braun — who has said he supports Kavanaugh — with suburban women. But the turmoil surrounding the nomination could also sting Donnelly if Democrats are seen as politicizing the allegation. Kavanaugh has denied the allegation.

For years, Republicans have insisted Donnelly's 2012 victory was a fluke caused by GOP nominee Richard Mourdock's incendiary comments about abortion and rape. Many now concede they underestimated Donnelly, who portrays himself as a conservative Democrat and often touts his votes for Trump's priorities.

While commuting back-and-forth between Indiana and Washington, Donnelly has held more than 190 campaign events since May — more than double the number attended by Braun, who resigned from his seat in the Indiana Legislature to focus on campaigning.

Bob Grand, a GOP fundraiser and Indiana powerbroker, said Donnelly has done a "phenomenal job" campaigning, but doubted it will be enough to win in an overwhelmingly Republican state.

"He's even featuring Donald Trump in his ads. What does that tell you?" Grand said.

Still, groups that have enthusiastically supported GOP nominees in the past are uncharacteristically absent.

In addition to the Indiana Chamber of Commerce, which opted against issuing an endorsement, the U.S. Chamber was mum over whether it will get involved. In 2016, the group spent at least $3.7 million backing GOP Sen. Todd Young in his race against Democrat Evan Bayh, a popular former Indiana governor and senator who previously worked for them.

Americans for Prosperity, the political arm of billionaire industrialists Charles and David Koch, interviewed Braun but decided not to directly support him. Two years ago, they launched a door-knocking and phone-bank operation that helped Young win.

On paper, Braun has everything the GOP wants: He built a national auto parts distribution company from the ground up, speaks with a subtle southern Indiana twang and is a virtual outsider to politics, despite his brief stint in the Legislature.

He also has the ability to self-fund.

During the GOP primary, Braun used his wealth, worth somewhere between $37 million and $95 million, to bury U.S. Reps. Todd Rokita and Luke Messer with more than $6.2 million worth of radio and TV spots, Federal Election Commission records show.

But Braun — whose wife once described him to The Indianapolis Star as the "tightest guy I know" — said after his May 8 victory that he wasn't looking to do the same in the general election.

With November looming, his campaign only started to ramp up spending on TV ads this week. Meanwhile, Democratic groups and super PACs are set to spend $22 million, much of it ruthlessly attacking Braun's business record.

They've seized on stories by the AP that revealed his companies racked up safety violations and were sued by employees for unfair treatment, including a worker kicked off health insurance days after he suffered a heart attack .

Democrats also labeled Braun a hypocrite for attacking Donnelly's family business for outsourcing jobs to Mexico while using Chinese goods for his own brand of auto accessories.

Republican outside groups, including a super PAC linked to Senate Majority Leader Mitch McConnell, have picked up the slack. They're on pace to pour at least $19 million into advertising. They've attacked Donnelly for being weak on immigration, voting against the Republican tax cut and being indecisive about whether he will support Kavanaugh.

But that may not matter if Braun doesn't campaign to win.

"I think Braun has a good narrative and a great story," said Kendall, the radio producer. "But he needs to be out there telling it."

FILE - This May 8, 2018 file photo Republican Senate candidate Mike Braun thanks supporters after winning the republican primary in Whitestown, Ind. Braun often refers to his rival, Democratic Sen. Joe Donnelly, as “Sleepin’ Joe,” but it’s actually Braun’s own sleepy campaign that has Republicans worried. Groups that typically back GOP candidates are sitting on the sidelines. Braun’s recent three-stop “solutions” tour across the state in a used RV was dwarfed by Donnelly’s seven-day, 40-stop trek in August. (AP Photo/Michael Conroy, File)

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